Studies are in progress to examine parathyroid hormone calcitonin interrelationship in the pregnant subhuman primate utilizing the interplacental vessels to serve as an access route to fetal samplings, in vivo. Fetal and neonatal monkey pancreases derived from these preparations are then enzymatically dissociated and the pancreatic islets are submitted to long term maintenance in tissue cultures. Studies of structure function interrelationship of the alpha, beta and delta cells and factors influencing proliferation of the endocrine cells in culture are in progress.